Eye tracking is a process of tracking the motion of one or both of a person's eyes relative to the person's head. Based on acquired information of the eye positions, eye tracking can be used as one type of input for human-computer interaction. One method of eye tracking is based on video oculography (VOG). VOG is a non-invasive, video based method of measuring eye motion. Light (e.g., infrared light) illuminates an eye and is reflected from the eye. A video camera senses the reflected light and records images of the eye. Based on the images of the eye, the eye tracking system recognizes the pupil and tracks locations of the center of the pupil over time. However, the computing power needed for tracking the pupil in the images usually causes latency. Furthermore, the light source, video camera and processor of the eye tracking system consume a notable amount of power.